The invention relates to a radial press for workpieces with cylindrical outer surfaces, particularly for securing fittings consisting of a sleeve and nipple to flexible pipes by mechanically altering the shape of the sleeve from that of the flexible pipe located between the nipple and the sleeve, which press consists of: a plurality of pressing tools which are arranged in a circle, are radially movable towards the outer surface of the workpiece and have outer surfaces, the generatrices of which extend towards the axis at an angle other than 90 degrees; a pressure ring which co-operates with the outer surfaces, is axially displaceable relative to the outer surfaces, and has a complementary inner surface; an axially extending backing member for the pressing tools; and a pressure-medium drive for imparting radial movement to the pressing tools.
In radial presses of this kind, the pressing tools execute a radial stroke, which is determined by the setting angle of the inner surface of the pressure ring in relation to the axis of the workpiece, as well as by the axial stroke of the pressure ring. However, these values cannot be varied to the required extent. The required radial pressing force is determined by the deformability of the workpiece. Although a very sharp setting angle of the slide facer of the pressing tools and the pressure ring results in low pressures in the hydraulic fluid because of the high transmission ratio necessitated thereby, a long axial stroke of the pressure ring is rendered necessary. For a given cross-section of the piston of the pressure-medium drive, this in turn calls for a large delivery capacity of the pump system accompanied by suitable selection of the flow cross-sections. On the other hand, the cycle would extend over unacceptably lengthy periods. Although, with a wide setting angle of the slide faces of the pressing tools and the pressure ring, the radial stroke of the pressing tools would be longer and the axial stroke of the pressure ring shorter, the changed transmission ratio requires higher pressure in the hydraulic system.
For certain applications, for example for connecting fittings to high-pressure flexible pipes, a long radial stroke by the pressing tools is necessary in order, for example, to permit fittings having a large diameter of connecting flange and/or a curved tubular connector to be introduced into the radial press. On the one hand, this determines the radial stroke of the pressing tools that is needed; on the other hand, the required radial pressure forces, in conjunction with the need for the lowest possible maximum pressure in the hydraulic system, determine the setting angle of the slide faces of the pressing tools and the pressure ring, which angle should be as sharp as possible in relation to the axis of the outer surface of the workpiece. The requirements imposed lead to diametrically opposed design solutions. The most appropriate solution would be to design a pressure ring, the setting angle of the inner surface of which is sharp, and which is capable of executing a correspondingly long axial stroke. Here, it has to be borne in mind that the stroke of the pressure ring as far as the point at which the pressing tools are applied to the workpiece would be an idling stroke for the most part, whereas the delivery capacity of the required hydraulic pump would have to be rated to suit the remaining part of the stroke known as the working stroke. Because of the necessarily large delivery volume during the idling stroke, either unacceptably lengthy times for carrying out the cycle or correspondingly large hydraulic pumps and flow cross-sections would be necessary. The normal delivery capacity for a radial press for connecting flexible pipe fittings having an outside diameter of 90 mm is in the order of 70 liters per minute.
DE-PS No. 22 14 339 has disclosed a solution to the problem in question which consists in making the pressure ring for the pressing tools axially displaceable independently of the pressure-medium drive. In this known case, the pressure ring is rendered axially displaceable by arranging it in a press frame in which it can be moved by hand with the aid of a screw-thread. For the purpose of introducing a fitting for a flexible pipe, the movable part of the press frame is first displaced hydraulically as far as the stop, whereafter the pressure ring is screwed out by hand until the pressing tools reach their extreme outer position. This procedure is repeated in reverse when establishing the connexion between the fitting and the flexible pipe. The known solution has given excellent results when used for repairs wherein a low total weight of equipment takes precedence over short cycle times. The known radial press is less suitable for full-scale production processes.
For the purpose of facilitating the introduction of fittings and flexible pipes, radial presses for full-scale production purposes have also been designed wherein the press as such is radially divided and the two parts are hinged to each other. However, this results in a reduction in the strength of the important components of the press. In particular, the front plate of the press, which must also take up the reaction forces of the entire press frame, has to be slotted, and this necessitates a complicated construction for enabling the necessary strength to be provided. Because of the need for swinging up the press tool when loading the press, valuable time in the production process is furthermore lost.